1. Field of Invention
The present invention relates to an air conditioning system, and more particularly to an air conditioning system capable of adjusting temperature through a secondary circulation.
2. Related Art
Variable Refrigerant Volume (VRV) also known as Variable refrigerant flow (VRF) consists of a number of air handling units connected to a modular external condensing unit, and allows refrigerant flow to be varied using either an inverter controlled variable speed compressor, or multiple compressors of varying capacity in response to changes in the cooling or heating requirements within the air conditioned space. A sophisticated control system enables switching between the heating and cooling modes. This type of system requires no internal plant room space and offers great flexibility through the many types of air handling units available. Applications vary from office, retail, hotel, luxury apartments, industrial, new and retrofitted buildings.
However, as the outdoor unit and the indoor units of the conventional VRV air conditioning system belong to the same circulation, i.e., the outdoor unit and the indoor units are all located in the same refrigerant circulation loop, the conventional VRV air conditioning system has the following problems in operation.
Generally, in order to make the compressor operate normally, in the prior art, a lubricant is used to lubricate the compressor. As the lubricant applied to the compressor usually exists in an oil tank of the compressor or in the refrigerant circulation system in a liquid state, and the refrigerant returning to the compressor after passing through the evaporator is usually in a vapor state. When the compressor is in operation, a part of the lubricant is usually discharged from the compressor with the refrigerant. As the outdoor unit and the indoor units of the conventional VRV air conditioning system all belong to the same circulation, the lubricant carried out of the compressor flows in the circulation refrigeration system with the refrigerant.
To solve the above problem, in the prior art, a device is added to the refrigeration system for retaining lubricant (for example, a high-efficiency oil separator is mounted at the outlet of the refrigerant on the compressor, so as to intercept the lubricant and prevent the lubricant from being carried out of the compressor with the vaporous refrigerant), or a more complicated control method is employed (for example, the running speed of the compressor is increased under a low load and at a specific time to accelerate the flow of the refrigerant, thus providing adequate vapor velocity to assure oil return), such that the lubricant flows back to the compressor. However, such a design makes the system more complicated.
The aforementioned refrigerating circulation is generally used in a large building, and thus the compressor is placed above the evaporator by 30 meters or even higher. When the height difference between the evaporator and the compressor is too big or the compressor is unloaded due to lower cooling demands from the air conditioned object, the vaporous refrigerant may not carry the lubricant any longer due to insufficient velocity of vapor flowing through the suction line, so that the lubricant is accumulated within the refrigerating tubes and the pipes and progressive loss of oil from the compressor. Insufficient oil is left to properly lubricate and cool the compressor, thereby causing the compressor to fail. As a result, a vertical restraint of the piping design in the prior art appears.
Similarly, when the horizontal length of the pipe is too long, the vaporous refrigerant may not carry the lubricant any longer due to insufficient velocity of vapor flowing through the suction line, so that the lubricant is easily accumulated within the refrigerating tubes and pipes. As a result, a horizontal restraint of the piping design in the prior art appears.